Endogenous viral elements are targeted by RNA silencing pathways in banana

Area of Science:

• Plant Virology
• Epigenetics
• Genomics

Background:

• Endogenous banana streak viruses (eBSV) integrated into banana genomes can cause disease in certain hybrids.
• Musa balbisiana (BB) genomes contain eBSV loci but are resistant to banana streak disease.
• The regulatory mechanisms controlling eBSV activity in BB plants remain unclear.

Purpose of the Study:

• To investigate the epigenetic regulation of endogenous banana streak viruses (eBSV) in Musa balbisiana (BB) banana plants.
• To understand how eBSV is silenced and why BB plants exhibit resistance to viral reactivation.

Main Methods:

• Comparative analysis of eBSV-free (Musa acuminata AAA) and eBSV-containing (BB and AAB) banana plants.
• High-throughput sequencing (Illumina) to analyze small interfering RNAs (siRNAs) and transcripts.
• Bisulfite sequencing to assess DNA methylation patterns across eBSV loci.

Main Results:

• eBSV loci produce low-abundance transcripts and predominantly 24-nt siRNAs, primarily from duplicated viral sequences.
• Extensive DNA methylation (CG, CHG, CHH contexts) was observed in both siRNA-accumulating and non-accumulating eBSV regions in BB plants.
• eBSV regulation in BB diploids appears to be primarily epigenetic.

Conclusions:

• Epigenetic control, particularly DNA methylation, effectively silences eBSV in Musa balbisiana (BB) diploids.
• This epigenetic silencing prevents viral awakening and systemic infection, contributing to inherent resistance.
• Findings have implications for managing integrated viruses in other plant systems.